Severe Heart failure kills 100,000 Americans yearly. Heart transplants are effective but scarce; medicines are available but - eventually - ineffective. A conceptually attractive answer, mechanical device 'destination therapy', is critically limited by power sources: present ones simply aren't compatible with safety in people restored to mobile, fully active lives - a clear goal of these devices. In turn, a conceptually attractive answer to this power problem, skeletal muscle harnessing, is critically limited by failure of force- transferring muscle-to-prosthesis interfaces. We've solved this. The MyoCouplerTM uses a myriad of extremely fine polymer fibers, dispersed very distally in the muscle, reducing interface stress from > 10,000 mmHg (conventional sutures and clamps) to the existing interstitial muscle pressure. Phase I proved feasibility; an independent group reproduced results in a different animal model. Further, our Phase II contracting research partner developed a hydraulic transfer system that is - except for this failing-interface dilemma - efficient, effective, and reliable. Specific aims are: 1) designing and documenting a device complying with regulatory standards, 2) systematically testing it, and 3) demonstrating long-term reliability of cyclic energy transfer using a validated in vivo model. Results will enable the next commercialization step - a GLP animal study. Truly self-contained mechanical support will then be realistic.